The process of planning interventions with a fixed instrument, for example an aspiration needle, based on pre-interventionally recorded data sets, is already known. These data sets can be obtained by 3D angiography, CT or MR investigation. The planning undertaken in advance can then be transferred to a navigation system or a system for orientation of the fixed instrument or the aspiration needle. Such a system is for example a stereotactic frame, which allows pinpoint alignment and positioning of the aspiration needle. The case can arise however in which the aspiration needle or another fixed instrument has to pass within a very short distance of critical structures such as vertebrae, organs or blood vessels. In order not to endanger the patient a continuous monitoring of the position of the needle is necessary. The direction of projection must be defined within the context of pre-interventional planning. The direction of projection, which can be imagined as a straight line through the tube focus and the center of the detector of the fluoroscopy system, is set by corresponding positioning of the C-arm of the fluoroscopy device. This setting is made manually, based on the experience of the operator, with a number of steps sometimes being required. The disadvantage in this case however is that the choice of the best direction of projection and the setting of the C-arm position and the multi-stage optimization which may be required are undertaken during fluoroscopy so that the patient is subjected to a certain dose of radiation even before the actual intervention.